Devices of the aforesaid type are disclosed, for instance, in DE 42 19 889 A1, EP 1 8013 300 A1, and U.S. Pat. No. 6,880,404 B2.
Such devices make possible the measurement of pressure in fluid lines, in particular in synthetic hoses that are used in medical technology in extracorporeal hose systems or hose assemblies for conducting or transporting fluids.
Fluids may include, for instance, medical irrigation fluids like salt solutions used for cleansing the interior of a body cavity or of a joint. Other possibilities of fluids include gasses or gas mixtures that, for instance, are used for insufflation of the abdominal cavity in the relation to a laparoscopic procedure.
The hose system or hose assembly is connected with a medical device, for instance a roller pump or insufflator, to conduct the fluid.
A hose assembly can comprise the following components:                a connection to a supply reservoir, in which the fluid to be conducted is stored, for instance a sack for liquids        a hose segment, composed of more resistant synthetic material, which is inserted into the medical device        additional synthetic hoses, used for instance for conducting the fluid in or out        connector elements (connectors) for the hose segment and for conducting the fluid in or out        a connection to a trocar of an endoscope        
Parts of the hose assembly or the entire hose assembly can be configured as one-time disposable articles or as reusable items.
The hose assembly must be sterile because it is connected to an instrument whose distal end is to be inserted into a patient's body cavity. Therefore no measurement devices connected to the hose assembly must be allowed to affect the sterility of the interior of the hose assembly. This requirement can be fulfilled by ensuring that the complete measurement device is in sterile condition. However, this involves the problem of having to ensure the sterility of the entire signal transmission pathway from the interior of the hose assembly all the way to the recording unit. In addition, said recording unit itself, for instance a transducer, must be of sterile configuration. This leads to the disadvantage of increased production and operating costs for the measurement device.
Alternatively, the signal transmission pathway contains an interface between a sterile part and a part that is not required to be of sterile configuration. The sterilize part of the signal transmission pathway picks up the signal that is to be measured, for instance the fluid pressure, in the interior of the hose assembly and conducts it onward to the interface. Thanks to the interface, the interior of the hose assembly is sterile and isolated from the environment. The recording unit and the part of the signal transmission path between the interface and the recording unit can be of non-sterile configuration. Consequently, substantial savings in cost and complex arrangements can be achieved, because a semiconductor pressure sensor, for instance, is not required to be of designed and built so that it is autoclavable. The problem with this alternative approach consists in providing an appropriate interface which ensures good signal transmission and seals off the sterile interior of the hose assembly. The interface must constitute an essentially impenetrable barrier for pathogenic germs.
The aforementioned documents U.S. Pat. No. 6,880,404 B2, DE 42 19 889 A1, and EP 1 813 300 A1, disclose devices that comprise a fluid chamber. The fluid chamber is configured as a flow-through chamber, which is connected at both the fluid ingress end and the fluid egress end with a fluid line that can be part of a hose assembly. The fluid chamber is provided with a wall that is configured as a flexible membrane or shaped from elastic material.
The disadvantage of these embodiments is that the fluid chamber cannot be constructed of a material or in a production stage, which for instance is possible for an injection moulded piece of synthetic material.
In the device disclosed in U.S. Pat. No. 6,880,404 B2 another membrane is present, flush with the wall of the fluid chamber, and is a part of a housing that comprises a transducer. As a result, the measuring is mainly made possible both by positive pressures (excess pressure with respect to the ambient pressure) and by negative pressures (low pressure with respect to the ambient pressure).
The disadvantage of this embodiment, however, is that no hydraulically rigid power lock is provided by the transducer between the elastic wall of the fluid chamber and the membrane of the transducer housing. The recorded pressure in areas close to the ambient pressure is not linearly dependent on the pressure at which the fluid line is impacted. Consequently, precise measurements of negative or positive pressures are impossible in areas of the ambient pressure.
In the devices disclosed in DE 42 19 889 A1 and EP 1 8013 300 A1, the wall is positioned, separated by an intermediate space, opposite a transducer. The intermediate space can be evacuated, aerated, or drained of air, so that the wall and the transducer can be brought into power-locking connection. This makes possible a precise measurement of positive pressures and negative pressures in the area of the ambient pressure.
The disadvantage of this embodiment is that the intermediate space impacted with a vacuum or with low pressure, its insulations and feeder lines are difficult to keep clean. In addition, from the adjacent vacuum from the non-sterile environment, impurities can be suctioned into the intermediate space and thus endanger the sterility of the interior of the hose assembly.
It is the object of the present invention to improve a device for measuring pressure of the aforementioned type, which is intended in particular for use in minimally invasive surgery, in such a way that one of the aforementioned disadvantages of the known devices is avoided. Precise measurement of the pressure should become possible in areas close to the ambient pressure. The cleanliness of the device and the sterility of the fluid should be ensured in appropriate ways.